Speedup access to SQL Server on Linux

Workaround for dotnet/corefx#24480 until the next version of corefx/sqlclient.

Fixes #1639

Author: ngbrown

.travis.yml

@@ -7,7 +7,7 @@ services:
   - postgresql
   - docker
 env:
-  - DB=SqlServer2008 CONNECTION_STRING="Server=localhost;initial catalog=nhibernate;User Id=sa;Password=P@ssw0rd;"
+  - DB=SqlServer2008 CONNECTION_STRING="Server=localhost;initial catalog=nhibernate;User Id=sa;Password=P@ssw0rd;packet size=4096;"
   - DB=PostgreSQL CONNECTION_STRING="Host=localhost;Port=5432;Username=postgres;Database=nhibernate;Enlist=true;"
   - DB=Firebird 
   - DB=MySQL CONNECTION_STRING="Server=127.0.0.1;Uid=root;Database=nhibernate;Old Guids=True;"